Signal Too Low. Permanent Fault

Other Diagnostic Trouble Codes
- Read off other diagnostic trouble codes (DTCs).
- Are EFI-541 and EFI-447 stored?

Yes:
^ Proceed to: Checking Fuse 3 section below.

No:
^ Proceed to: Checking Power Cable section below.





Checking Fuse 3
- Ignition OFF.
- Check that fuse 3 (11B/3) is intact.

If reading is OK:
^ Proceed to: Checking Voltage to Fuse 3 section below.

If reading is incorrect:
^ Check circuit after fuse 3 for a short-circuit to ground. For further information about the circuit, see the Wiring Diagram.
^ Proceed to: Verification section below.





Checking Voltage to Fuse 3
- Ignition ON.
- Fuse 3 (11B/3) removed.
- Connect a voltmeter between the rear output on the fuse holder for fuse 3 (11B/3) and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Check cable between fuse 3 and heated oxygen sensor (HO2S) connector terminal 1 for an open-circuit.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Check cable between fuse 3 and main relay (2/32) terminal 3 for an open-circuit.
^ Proceed to: Verification section below.





Checking Power Cable
- Ignition OFF.
- Disconnect heated oxygen sensor (front heated oxygen sensor: blue connector, rear heated oxygen sensor: black connector).
- Ignition ON.
- Connect a voltmeter between heated oxygen sensor connector terminal 1 (main relay 2/32 side) and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Proceed to: Checking The Signal Cable section below.

If reading is incorrect:
^ Check cable between heated oxygen sensor terminal 1 and main relay (2132) terminal 3 for an open-circuit.
^ Proceed to: Verification section below.





Checking The Signal Cable
- Ignition ON.
- Heated oxygen sensor disconnected.
- Connect a voltmeter between the heated oxygen sensor connector terminal 2 (engine control module (ECM) side) and ground.
- The voltmeter should read approx. 0 Volts.

If reading is OK:
^ Proceed to: Checking Signal Cable Resistance to Ground section below.

If Reading Is Incorrect:
^ Check cable between heated oxygen sensor terminal 2 and engine control module # A29 for a short-circuit to supply voltage.
^ Proceed to: Verification section below.





Checking Signal Cable Resistance To Ground
- Ignition OFF.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Heated oxygen sensor disconnected.
- Disconnect engine control module Connect an ohmmeter between heated oxygen sensor connector terminal 2 (engine control module side) and ground.
- The ohmmeter should read infinite resistance.

If reading is OK:
^ Proceed to: Checking Signal Cable Resistance section below.

If reading is incorrect:
^ Check cable between heated oxygen sensor terminal 2 and engine control module # A29 for a short-circuit to ground.
^ Proceed to: Verification section below.





Checking Signal Cable Resistance
- Ignition OFF.
- Heated oxygen sensor disconnected.
- Engine control module disconnected.
- Connect the breakout box and check ground terminals.
- Connect an ohmmeter between heated oxygen sensor connector terminal 2 (engine control module side) and breakout box terminal # 29 (# A 29).
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to: Checking Heated Oxygen Sensor section below.

If reading is incorrect:
^ Check cable between heated oxygen sensor terminal 2 and engine control module # A29 for an open-circuit.
^ Proceed to: Verification section below.





Checking Heated Oxygen Sensor
- Ignition OFF.
- Connect the heated oxygen sensor.
- Engine control module disconnected. Connect an ohmmeter between breakout box terminals # 27 (# A27) and # 29 (# A29).
- The ohmmeter should read approx. 1.5 - 13 ohms.

If reading is OK:
^ The cause of the diagnostic trouble code has been loose connections in the rear heated oxygen sensor connector.
^ Check that the pins in the connector are intact.

NOTE: Do not apply rust solvent spray or grease to the heated oxygen sensor connector.

^ Proceed to: Verification section below.

If reading is incorrect:
^ Try a new heated oxygen sensor.
^ Proceed to: Verification section below.





Verification
After carrying out the repair, check that the fault has been remedied as follows:

- Ignition OFF.
- Front and rear heated oxygen sensors connected.
- Engine control module connected.
- Stan the engine and idle it.
- Go into diagnostic test mode menu.
- Watch the diagnostic trouble code to be verified.
- Wait until its status switches to tested. This can take up to 15 minutes.
- Read diagnostic trouble codes.
- If EFI-521 or EFI-522 are stored they should intermittent fault status.

If reading is OK:
^ Fault corrected.

If reading is incorrect:
^ Proceed to: Fault-tracing Information section below.

Fault-tracing Information
The verification result shows that the fault persists.

- Do you want to exit fault-tracing?

Yes:
^ Fault not corrected.

No:
^ Proceed to: Other Diagnostic Trouble Codes section above.